There is only call by value in java, not call by reference. If we call a method passing a value, it is known as call by value. The changes being done in the called method, is not affected in the calling method.

Table of Contents

Example of call by value in java

In case of call by value original value is not changed. Let’s take a simple example:
1. class Operation{
2. int data=50;
3.
4. void change(int data){
5. data=data+100;//changes will be in the local variable only
6. }
7.
8. public static void main(String args[]){
9. Operation op=new Operation();
10.
11. System.out.println(“before change “+op.data);
12. op.change(500);
13. System.out.println(“after change “+op.data);
14.
15. }
16. }

Output:before change 50
after change 50

Another Example of call by value in java

In case of call by reference original value is changed if we made changes in the called method. If we pass object in place of any primitive value, original value will be changed. In this example we are passing object as a value. Let’s take a simple example:
1. class Operation2{
2. int data=50;
3.
4. void change(Operation2 op){
5. op.data=op.data+100;//changes will be in the instance variable
6. }
7.
8.
9. public static void main(String args[]){
10. Operation2 op=new Operation2();
11.
12. System.out.println(“before change “+op.data);
13. op.change(op);//passing object
14. System.out.println(“after change “+op.data);
15.
16. }
17. }
Output:before change 50
after change 150

Java Strictfp Keyword

Java strictfp keyword ensures that you will get the same result on every platform if you perform operations in the floating-point variable. The precision may differ from platform to platform that is why java programming language have provided the strictfp keyword, so that you get same result on every platform. So, now you have better control over the floating-point arithmetic.

Legal code for strictfp keyword

The strictfp keyword can be applied on methods, classes and interfaces.
1. strictfp class A{}//strictfp applied on class
1. strictfp interface M{}//strictfp applied on interface
1. class A{
2. strictfp void m(){}//strictfp applied on method
3. }

Illegal code for strictfp keyword

The strictfp keyword cannot be applied on abstract methods, variables or constructors.
1. class B{
2. strictfp abstract void m();//Illegal combination of modifiers
3. }
1. class B{
2. strictfp int data=10;//modifier strictfp not allowed here
3. }
1. class B{
2. strictfp B(){}//modifier strictfp not allowed here
3. }

Java instanceof

The java instanceof operator is used to test whether the object is an instance of the specified type (class or subclass or interface).
The instanceof in java is also known as type comparison operator because it compares the instance with type. It returns either true or false. If we apply the instanceof operator with any variable that has null value, it returns false.

Simple example of java instanceof

Let’s see the simple example of instance operator where it tests the current class.
1. class Simple1{
2. public static void main(String args[]){
3. Simple1 s=new Simple1();
4. System.out.println(s instanceof Simple1);//true
5. }
6. }

Output:true

An object of subclass type is also a type of parent class. For example, if Dog extends Animal then object of Dog can be referred by either Dog or Animal class.

Another example of java instanceof operator

1. class Animal{}
2. class Dog1 extends Animal{//Dog inherits Animal
3.
4. public static void main(String args[]){
5. Dog1 d=new Dog1();
6. System.out.println(d instanceof Animal);//true
7. }
8. }

Output:true

instanceof in java with a variable that have null value

If we apply instanceof operator with a variable that have null value, it returns false. Let’s see the example given below where we apply instanceof operator with the variable that have null value.
1. class Dog2{
2. public static void main(String args[]){
3. Dog2 d=null;
4. System.out.println(d instanceof Dog2);//false
5. }
6. }

Output:false

Downcasting with java instanceof operator

When Subclass type refers to the object of Parent class, it is known as downcasting. If we perform it directly, compiler gives Compilation error. If you perform it by typecasting, ClassCastException is thrown at runtime. But if we use instanceof operator, downcasting is possible.
1. Dog d=new Animal();//Compilation error
If we perform downcasting by typecasting, ClassCastException is thrown at runtime.
1. Dog d=(Dog)new Animal();
2. //Compiles successfully but ClassCastException is thrown at runtime

Possibility of downcasting with instanceof

Let’s see the example, where downcasting is possible by instanceof operator.
1. class Animal { }
2.
3. class Dog3 extends Animal {
4. static void method(Animal a) {
5. if(a instanceof Dog3){
6. Dog3 d=(Dog3)a;//downcasting
7. System.out.println(“ok downcasting performed”);
8. }
9. }
10.
11. public static void main (String [] args) {
12. Animal a=new Dog3();
13. Dog3.method(a);
14. }
15.
16. }

Output:okdowncasting performed

Downcasting without the use of java instanceof

Downcasting can also be performed without the use of instanceof operator as displayed in the following example:
1. class Animal { }
2. class Dog4 extends Animal {
3. static void method(Animal a) {
4. Dog4 d=(Dog4)a;//downcasting
5. System.out.println(“ok downcasting performed”);
6. }
7. public static void main (String [] args) {
8. Animal a=new Dog4();
9. Dog4.method(a);
10. }
11. }

Output:okdowncasting performed
Let’s take closer look at this, actual object that is referred by a, is an object of Dog class. So if we downcast it, it is fine. But what will happen if we write:
1. Animal a=new Animal();
2. Dog.method(a);
3. //Now ClassCastException but not in case of instanceof operator

Understanding Real use of instanceof in java

Let’s see the real use of instanceof keyword by the example given below.
1. interface Printable{}
2. class A implements Printable{
3. public void a(){System.out.println(“a method”);}
4. }
5. class B implements Printable{
6. public void b(){System.out.println(“b method”);}
7. }
8.
9. class Call{
10. void invoke(Printable p){//upcasting
11. if(p instanceof A){
12. A a=(A)p;//Downcasting
13. a.a();
14. }
15. if(p instanceof B){
16. B b=(B)p;//Downcasting
17. b.b();
18. }
19.
20. }
21. }//end of Call class
22.
23. class Test4{
24. public static void main(String args[]){
25. Printable p=new B();
26. Call c=new Call();
27. c.invoke(p);
28. }
29. }

Output: b method

So, this brings us to the end of blog. This Tecklearn ‘Call by Value and Call by Reference in Java’ blog helps you with commonly asked questions if you are looking out for a job in Java Programming. If you wish to learn Java and build a career Java Programming domain, then check out our interactive, Java and JEE Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:

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